1. Field of the Invention
This invention relates to a valve device for controlling liquid flow, in particular for use in filling a carton.
2. Description of the Prior Art
Various valve devices for filling containers are known. French Patent Application Publication No. 2299628 and U.S. Pat. Nos. 3949791 and 4079762 disclose a variety of possible constructions of such devices.
Published British Patent Specification 2043604A discloses a filling valve device for pressurized fluids which comprises a nozzle containing a stem axially displaceable downwardly under the thrust of the fluid against the bias of a helical spring closely encircling the stem. The stem carries an obturating dish at the top and a valve closure head at the bottom, the dish dividing the nozzle interior into two spaces, one communicating with a source of pressurized fluid, the other communicating with the interior of the container to be filled whenever the valve closure head is depressed.
Contact of the fluid with air exterior to the nozzle is prevented and possible foam formation is discharged through an axial passageway formed through the stem and through an elbow conduit coaxial with the stem axis and aligned with the central bore of the stem. The spring acts between the underside of the dish and the top of a horizontal spider mounted in the interior of the nozzle, the spider being composed of a central, stem-guiding ring having radial spokes which rest against a step formed in the internal surface of the nozzle. Below the spider, the internal surface of the nozzle converges downwardly at a substantial angle to the nozzle axis. In the open condition of the valve device, the liquid flows down through between the obturating dish and the internal surface, past the outside of the spring, and through the spokes of the spider. The valve head, which protrudes downwardly from the outlet end of the nozzle, carries a gasket for bearing upwardly against that outlet end to seal the same.
A problem with this device is that the close encircling of the stem by the spring and the use of a spider and a sealing gasket provide crevices where solids content can accumulate and be very difficult to remove by flushing of the device.
Published European Patent Application 0090664 discloses a valve device for use in filling cartons, which includes a metal tubular housing containing a metal valve member comprising a closure part co-operating with a metal valve seat at the lower extremity of the housing, and a driving part movably received with clearance in the housing. In one embodiment, the internal surface of the upper part of the housing is co-axial with the housing and comprises, progressing downwards, a cylindrical zone, followed by a downwardly diverging frusto-conical zone at about 10.degree. to the axis of the housing, followed by a substantially radially inwardly directed annular zone, followed by a rectangular two sided annular groove which receives the lowermost coil of, and thereby locates the lower end of, a downwardly-diverging, conical compression spring co-axial with the housing. In another embodiment, the cylindrical zone is followed by a downwardly diverging frusto-conical zone at about 2.degree. to the axis, followed by a second cylindrical zone, itself followed by the frustoconical zone at about 10.degree. to the axis. Owing to the provision of the frusto-conical zone at about 10.degree. to the axis, during the later part of the opening movement of the valve member against the spring, the clearance between the driving part and the housing increases smoothly and considerably, and the driving part reaches a force equilibrium position at which the clearance is considerable. Two grooves formed in the housing and the closure part immediately below the valve seat bound an annular closed space for receiving liquid squeezed out downwardly at the valve seat as the closure part closes. Four equiangularly spaced fins extending upwards from the closure part support a co-axial tubular part which is a sliding fit in the housing and which terminates short of the closure part to leave liquid outlets.
The smoothly and considerably increasing clearance is intended to enable the valve device to cope with liquids of considerably differing viscosity. However, it has been found in practice that only a relatively limited range of viscosities can be coped with without replacement of parts. For example, it is desirable for such valve devices to be able to cope with a range of viscosities increasing from 3% fat milk, through 10% fat cream, through drinking yogurt, to natural yogurt with small fruit pulp. Yet, it has been found in practice that the valve device of EP00090664 requires the provision of a selection of driving parts of differing maximum external diameters in order to be able to cope with such a range of viscosities. However, with aseptic filling, dismantling of the filler in order to change from filling one liquid product to filling another is highly undesirable. The provision of the frusto-conical zone at about 2.degree. to the axis followed by the second cylindrical zone does not assist in this respect, because these two zones are intended to provide a slight clearance relative to the driving part to ensure that, during the major part of the closing stroke of the valve member, liquid trapped between the driving part and a non-return valve upstream of the valve device can rapidly escape to below the driving part; the driving part is not intended to have an equilibrium position at either of these two zones. Another difficulty which has been found to arise in practice with the valve device of EPO090664 is that the liquid, having passed through the clearance between the driving part and the frustoconical zone at about 10.degree. to the axis, not only finds itself having to turn through more than 90.degree. owing to the presence of the substantially radial annular zone, but, as it encounters the lowermost coils of the spring, which collapse first during compression of the conical spring, the liquid then has to climb upwards over these substantially closed lowermost coils until it can penetrate through between higher coils of the spring. This may not constitute a problem with liquid of relatively low viscosity, for example 3% fat milk, but it proves an excessive obstruction for liquid of relatively high viscosity, such as natural yogurt with small fruit pulp. A further difficulty with the valve device of EP0090664 is that, with use, and particularly with liquids with a relatively high solid content, the two grooves formed in the housing and the closure part immediately below the valve seat become gradually clogged with solids. This results in the grooves not properly performing their function of trapping liquid squeezed out downwardly at the valve seat, with consequent dripping, and/or the closure part being obstructed from closing fully, resulting in leakage and consequent dripping. A yet further difficulty is that the use of four fins can produce problems in accurate centering of the valve member in the housing and also requires the valve member to have some means for retaining the valve member against turning relative to the housing around the axis, because the four liquid flows among the fins at the closure part tend to assume a squarish outline as seen in plan, so that there would be a risk that some of the liquid might miss a square-section carton at the corners of the squarish outline unless that outline is held substantially in register with the plan outline of the carton. A still further difficulty is that the manufacturing tolerances required to achieve a liquid-tight seal with a metal-to-metal seating are very high and, moreover, a metal-to-metal seating is unable to adapt itself sealingly to solid particles becoming deposited therebetween.